Obesity has been linked to a wide range of conditions. Now a new study has linked high body mass index (BMI) to an increased risk of developing the most common cancer. The study, published in the Lancet journal, involved more than 5 million adults.

The researchers identified 5.24 million individuals aged 16 and older who were cancer free and followed them for approximately 7.5 years in Britain.

The risk of developing 22 of the most common cancers, representing 90% of the cancers diagnosed was measured according to BMI after adjusting for individual factors such as age, sex, smoking status, and socioeconomic status. In this study a total of 166 955 people developed one of the 22 cancers studied over the follow-up period. BMI was clearly associated with 17 out of the 22 specific types of cancer examined.

The results reveal that each 5 kg/m² increase in BMI was clearly linked with higher risk of cancers of the uterus (62% increase), gallbladder (31%), kidney (25%), cervix (10%), thyroid (9%), and leukemia (9%). Higher BMI also increased the overall risk of liver (19% increase), colon (10%), ovarian (9%), and breast cancers (5%), but the effects on these cancers varied by underlying BMI and by individual-level factors such as sex and menopausal status. Even within normal BMI ranges, higher BMI was associated with increased risk of some cancers.

Dr Bhaskaran, the lead researcher, commented on the study: “There was a lot of variation in the effects of BMI on different cancers. For example, risk of cancer of the uterus increased substantially at higher body mass index; for other cancers, we saw more modest increases in risk, or no effect at all. For some cancers like breast cancer occurring in younger women before the menopause, there even seemed to be a lower risk at higher BMI. This variation tells us that BMI must affect cancer risk through a number of different processes, depending on the cancer type.”